Cascaded amplifier



Dec. 12, 1933. K. POSTHUMUS EI'AL CAS CADED AMPLIFIER Filed Jan. 2, 1932 s v 5% n M mm 8 V Hsd M OO R TPR o N o Em W n 1 KT Y B Patented Dec. 12, 1933 UNITED STATES PATENT OFFICE Weyers, Eindhoven,

of Delaware Application January 2,

and in Germany Claims.

This invention relates to a cascaded amplifier comprising tuned coupling transformers.

, For amplifying a more or less wide frequency a band with the simultaneous suppression of the 0 frequencies above and below this band cascaded amplifiers having tuned circuits may be used.

In this case it is desirable that the resulting resonance curve of such an amplifier resembles as much as possible a rectangle having the de- 310 sired band width as basis. For the purpose above referred to it is known to provide cascaded amplifiers, with transformers having tuned input and output circuits. The shape of the resonance curve of any of these transformers, and, also, of any coupling system depends on the coupling factor and on the damping of the circuits.

According to the invention a suitable form of the resonance curve of the whole system is obtained by coupling the tuned circuits of one of the transformers critically by damping them comparatively strongly whereas the circuits of the other transformer on the contrary are coupled hypercritically and damped slightly. By hypercritical coupling is to be understood the coupling factor between both tuned circuits at which the crest of the resulting resonance curve begins to sag.

The invention will be more clearly understood by reference to the accompanying drawing, representing, by way of example, one embodiment thereof.

Fig. 1 shows schematically a two stage medium, or intermediate, frequency amplifier,

Fig. 2 shows the resonance curves of both coupling transformers and the resulting curve.

In Fig. 1 the amplifying tubes of the amplifier arrangement are designated by V1, V2 and V3. Between these tubes are interconnected transformers T1 and T2 having windings, tuned by parallel condensers C, as coupling elements. The transformer T1 together with the condensers form the system I constituted by two coupled tuned circuits. The transformers T2 together with its condensers constitutes a similar system II.

The coupling of one of these systems, for instance system I, is made critical, whereas the system is comparatively highly damped (coupling factor k=0.04, damping decrement 1 0.04) The resonance curve of this system corresponds approximately to the curve a shown in Fig. 2. The coupling of the system II is chosen hypercritical (7c 0.10) and the damping is rendered weak (v=0.02). In this case the Netherlands, assignors to Radio Corporation of America,

a corporation 1932, Serial No. 584,436,

June 16, 1931 resonance curve of this system almost corresponds to the curve 1) represented in Fig. 2. The resulting resonance curve of the whole amplifier nearly corresponds to the shape of the curve 0 shown in Fig. 2, which rather approximates the most desirable rectangular shape.

While we have indicated and described one arrangement for carrying our invention into efiect, it will be apparent to one skilled in the art that our invention is by no means limited to the particular organization shown and described, but that many modifications may be made without departing from the scope of our invention as set forth in the appended claims.

What is claimed is:

1. A cascaded amplifier comprising at least three tubes, a pair of tuned circuits coupling the first two tubes, a pair of similarly tuned circuits coupling the last two tubes, the tuned circuits of one of said pairs being coupled to produce a double hump band pass characteristic and having a low amount of damping, and the tuned circuits of the other pair being coupled and damped in a manner such that its resonance curve characteristic combines with the other characteristic to produce an amplifier over-all band characteristic having a substantially flat top.

2. A cascaded amplifier comprising at least three tubes, a pair of tuned circuits coupling the first two tubes, a pair of similarly tuned circuits coupling the last two tubes, the tuned circuits of one of said pairs being coupled to produce a double hump band pass characteristic and having a low amount of damping, and the tuned circuits of the other pair being coupled and highly damped in a manner such that its resonance curve characteristic combines with the other characteristics to produce an amplifier over-all band characteristic having a substantially flat top.

3. A cascaded amplifier comprising at least three tubes, a pair of fixedly tuned circuits coupling the first two tubes, a pair of similarly tuned circuits coupling the last two tubes, the tuned circuits of one of said pairs being coupled to produce a double hump band pass character istic and having a low amount of damping, and the tuned circuits of the other pair being coupled and clamped in a manner such that its resonance curve characteristic combines with the other characteristic to produce an amplifier over-all band characteristic having a substan tially flat top.

4. A cascaded amplifier comprising at least 5. A cascaded intermediate frequency' ampli fier comprising at least three tubes, a pair of tuned circuits coupling the first two tubes, a pair of similarly tuned circuits coupling the last two tubes, the tuned circuits of one of said pairs being inductively coupled to produce a double hump band pass characteristic and having a low amount of damping, and the tuned circuits of the other pair being inductively coupled and and damped in a manner such that its resonance curve characteristic combines with the other characteristic to produce an amplifier over-all 'band characteristic having a substantially fiat top.

' I KLAAS POSTHUMUS.

THEODOBUS JOSEPHUS WEYERS. 

